An elongated plate element, for example of aluminum oxide, or a metal plate which is coated with an insulator such as aluminum oxide, is retained within a hollow spark plug insulator (15) by a sealing mass (38), for example a sinter compound, sintering together the plate element (37) and the insulator body (35). The plate element carries a strip or conductive track layer electrode (25) thereon, located, for example, on one major surface of the plate; at the ignition end, the plate may have a through-hole (52), plated through, so that the ignition electrode will have conductive portions at both sides of the plate, faced by ground electrode portions which likewise can be retained on plate-like carrier elements, and connected to the metal housing (11) of the spark plug via conductive tracks (60, 61) and a conductive sealing ring (17"). The plates can carry heaters (32) and operation sensors, such as gas composition sensor, temperature sensor, pressure sensor or the like, which may, for example, have one electrode connected to ground or chassis, and hence to the metal housing, and the other electrode carried along in strip form to the connecting end portion of the spark plug. The plate and layer-like construction of the insulating elements permits modular combination of required components having the desired operating and/or sensing characteristics, and are suitable for mass production assembly.